Construction method for new underground structure

ABSTRACT

[Problem] An object of the present invention is to provide a construction method for a new underground structure, the method achieving reduction in the load imposition of a new underground framework on an existing underground concrete framework, and reduction in construction cost for constructing the new underground structure. 
     [Solving Means] A new underground structure  100  having a basement available as a residential space, and an underground pit which is an underground facility for housing piping equipment, etc., is constructed with a fluidized soil wall  300  held between an existing underground concrete framework  200  and a new underground concrete framework  400.

TECHNICAL FIELD

The present invention relates to a construction method for a newunderground structure, and in particular to a construction method for anew underground structure by which a reduction in the load imposition ofthe new underground structure on an existing underground structure and areduction in construction cost can be achieved.

BACKGROUND ART

When various structures, such as a building, are rebuilt, an existingstructure is required to be dismantled, but, when the existing structureis equipped with an underground structure, such as a basement floor, theexisting underground structure is also required to be dismantled.However, an underground exterior wall, a post, an underground beam, afoundation, and the like which constitute the existing undergroundstructure bear soil pressure from surrounding soil, and thereforehaphazard dismantlement may cause ground collapse, ground displacement,or the like, resulting in a considerable influence on neighboring areas.

Then, a method for newly building an underground structure withoutdismantling an existing underground structure is suggested in a patentdocument 1.

According to the construction method for an underground structuresuggested in the patent document 1, first, a strut is set up to afloor-height middle portion of an existing underground exterior wall ofthe first basement floor, and floor beams are removed while pressure isapplied to the strut in the direction of the exterior wall via by ajack. This series of operations are performed on each floor, a new wallis placed within the existing underground exterior wall so as toconstruct a combined wall with the existing underground exterior wall,and then the floor beams are removed. This series of operations areperformed on each floor so that a new underground structure isconstructed.

Patent Document 1: Japanese Patent Application Laid-open Publication No.2005-201007

SUMMARY OF THE INVENTION Problem to Be Solved by the Invention

According to the construction method for an underground structuredisclosed in the patent document 1, however, since the combined wall tobe constructed is for integrating the existing underground exterior walland a new wall with each other, the load imposition acting downstairsincreases. Therefore, a larger supporting force is required to supportthis load, which causes the problem of increasing construction cost.

The present invention has been made in view of these circumstances, andan object thereof is to provide a construction method for a newunderground structure, which can achieve reduction in the loadimposition of a new underground concrete framework on an existingunderground concrete framework, and reduction in construction cost forbuilding the new underground concrete framework.

Means for Solving the Problem

In order to achieve the above object, the present invention provides aconstruction method for a new underground structure by which a newunderground concrete framework is constructed without entirelydismantling an existing underground concrete framework, wherein: afluidized soil wall is constructed by filling an inner circumferentialface of the existing underground concrete framework with fluidized soil,and a new underground concrete framework is constructed on the innercircumferential face of the fluidized soil wall.

Further, in order to achieve the above object, the present inventionprovides a construction method for a new underground structure by whichan existing underground concrete framework is partially utilized toconstruct a new underground concrete framework without entirelydismantling and removing the existing underground concrete framework,the method including: vertically providing a first formwork body on aninner circumferential face of the existing underground concreteframework at a predetermined distance from the existing undergroundconcrete framework; filling a space between the existing undergroundconcrete framework and the first formwork body with fluidized soil toconstruct a fluidized soil wall; vertically providing a second formworkbody on an inner circumferential face of the fluidized soil wall at apredetermined distance from the fluidized soil wall; and castingconcrete in between the fluidized soil wall and the second formwork bodyto construct a new underground concrete framework.

In this case, it is desired that the first formwork body and the secondformwork body are kept upright by separators, and further it is desiredthat the first formwork body and the second formwork body are formworkpanels formed by bending and cutting a plate-like steel material into asubstantially rectangular front shape and a substantiallyangular-wave-like cross-sectional shape.

Advantageous Effects of the Invention

According to the present invention, since the new underground concreteframework formed within the existing underground concrete framework iscomposed of the fluidized soil wall and the new underground concreteframework when a new underground structure is constructed, the usage ofconcrete can be reduced as compared with the case where the newunderground concrete framework is composed of only the new undergroundconcrete framework. Further, since fluidized soil has a lower specificgravity than concrete, the load imposition of the new undergroundconcrete framework on the existing underground concrete framework can bereduced.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a construction method for a new underground structureaccording to an embodiment of the present invention will be describedwith reference to the drawings.

FIG. 1 is a vertical sectional side view showing the structure of a newunderground structure constructed by the construction method accordingto the embodiment.

As shown in FIG. 1, the underground structure constructed by theconstruction method according to the embodiment is a new undergroundstructure having a basement available as a residential space, and anunderground pit which is a facility for housing piping equipment or thelike, and the underground structure is constructed by holding afluidized soil wall 300 between an existing underground concreteframework 200 and a new underground concrete framework 400.

The underground pit in this underground structure is an undergroundspace for housing piping equipment or the like, but it is unnecessary toprovide the underground pit if the basement has a space for housingpiping equipment or the like. Further, though the underground structureshown in FIG. 1 is an underground structure having only a singlebasement floor, the number of underground floors may be plural, wherethe configuration and the construction method of a new undergroundstructure according to the present invention are not changed.

When an existing underground structure is dismantled, a post and thelike which were used to construct the underground structure aredismantled, and only the existing underground concrete framework 200composed of an existing beam 201, an existing load-bearing wall 202, andan existing foundation (foundation/underground beam) 203 remains.

Within this existing underground concrete framework 200, the fluidizedsoil wall 300 is constructed. This fluidized soil wall 300 isconstructed by filling with fluidized soil (backfill material that isslurry backfill soil which has been preliminarily blended with cement ina controlled manner in a plant and which is fluidized so that it can becast by a pump). Specifically, the fluidized soil wall 300 isconstructed by driving formwork panels 500 within the existingunderground concrete framework 200 at a predetermined distancetherefrom, keeping the formwork panels 500 upright by separators 501,filling a space between the formwork panels 500 and the existingunderground concrete framework 200 with the fluidized soil, andsolidifying the fluidized soil.

Then, a new framework, that is, the new underground concrete framework400, is constructed within the fluidized soil wall 300. The newunderground concrete framework 400 is composed of a new slab 401 whichconstitutes the floor of the basement and the ceiling of the undergroundpit, a new beam 402, and a new wall 403. This new underground concreteframework 400 is constructed by driving formwork panels 600 within thefluidized soil wall 300 at a predetermined distance therefrom, couplingthese formwork panels 600 with the formwork panels 500 of fluidized soilwall 300 described above by means of separators 601 to keep the formworkpanels 600 upright, and casting concrete in between the formwork panels500 of the fluidized soil wall 300 and the new formwork panels 600.

FIGS. 2 and 3 are views showing the configuration of the formwork panels500 and 600 used in the construction method for an underground structureaccording to the embodiment.

As shown in FIG. 2, the formwork panels 500 and 600 are left-in-placetype formwork panels formed by bending and cutting a plate-like steelmaterial into a substantially rectangular front shape and asubstantially angular-wave-like cross-sectional shape. Since thisformwork panel 500 is configured such that a plurality of ridges 11parallel to each other are formed at predetermined distances by bendinga panel steel plate into a substantially angular-wave-like crosssectional shape, resulting in reinforcement of the strength of the panelitself. Further, by forming the panel cross section into an equilateralangular-wave-like shape, the panel exerts excellent strength againstpressure on the front or back face of the panel.

It should be noted that, in the embodiment, a direction in which thisridges 11 are formed is defined as a longitudinal direction of theformwork panel 500, and a direction perpendicular to the longitudinaldirection is defined as a lateral direction of the formwork panel 500.

As shown in FIGS. 2 and 3, this ridge 11 is composed of a top face 31,and two side faces 32 provided so as to connect to the top face 31 inboth lateral directions thereof. Further, in a recessed face between therespective ridges 11, a plurality of ribs 12 raised in their lateralcross section and grooves 16 recessed in their lateral cross section arealternately formed in parallel to the ridges 11.

Further, in both ends of the ridge 11 in the panel lateral direction,that is, on boundary lines between the ribs 12 and the grooves 16adjacent to the ribs 12, slits 13 each having a predetermined length areprovided at predetermined distances like broken lines in parallel withthe ridges 11. By bending the formwork panel 500 at a predeterminedangle along this row of broken-line-like slits 13, a corner portion canbe formed in the formwork. Further, by bending the formwork panel 500along this row of broken-line-like slits 13 forward and backwardalternately and repeatedly, the formwork panel 500 can easily be cutinto a desired size.

This slit 13 is a slit having a very narrow width and a predeterminedlength and penetrating the formwork panel 500. This slit 13 is formed soas to have a width (clearance) and a length which allow discharge ofexcess water contained in concrete or fluidized soil but do not allowleakage of liquid concrete or fluidized soil from the slit 13 aftercasting of concrete or filling with fluidized soil.

The top face 31 of the ridge 11 is provided with a plurality offlap-like lids 14. By opening these lids 14, separator insertion holesare formed. By inserting the above-described separators 501 and 601 intothese separator insertion holes and fastening the separators together bya predetermined method, the formwork panels 500 and 600 can be keptupright.

FIG. 4 is a view showing an X-X section in FIG. 1.

As shown in FIG. 4, the new underground structure is a structure havingthe fluidized soil wall 300 between the existing underground concreteframework 200 and the new underground concrete framework 400.

In order to construct the fluidized soil wall 300, first, the formworkpanels 500 are driven, then anchors 307 are driven into the existingunderground concrete framework 200, then these driven anchors 307 arecoupled with the separators 501, then the formwork panels 500 are keptupright by these separators 501, and then the space between the formworkpanels 500 and the existing underground concrete framework 200 is filledwith fluidized soil, resulting in construction.

Washers 301 and 302 each having its both ends bent are provided atconnections between the formwork panels 500 and the separators 501. Thewasher 301 is provided on the back face of the formwork panel 500 (onthe side of the existing underground concrete framework 200), andfastened to the formwork panel 500 by a nut 303. The washer 302 isprovided on the front side of the formwork panel 500 (on the side of thenew underground concrete framework 400). The washer 302 is a washerwhich is long in the longitudinal direction, and fastened, by a long nut304, to a distal end of the separator 501 protruding from the formworkpanel 500. Then, the fluidized soil wall 300 is constructed by fillingthe space between the existing underground concrete framework 200 andthe formwork panels 500 with fluidized soil.

The new underground concrete framework 400, as described above, isconstructed by driving the new formwork panels 600 within the fluidizedsoil wall 300 at a predetermined distance therefrom, coupling theseformwork panels 600 with the formwork panels 500 for the fluidized soilwall 300 by means of the separators 601 so as to keep the formworkpanels 600 upright, and casting concrete in between the formwork panels500 of the fluidized soil wall 300 and the new formwork panels 600. Atthis time, the formwork panel 600 is kept upright by coupling one end ofthe separator 601 with the long nut 304 and coupling the other endthereof with the formwork panel 600, and a pipe 305 is provided on frontfaces of the formwork panels 600 and fixed thereto by form ties 306. Inthis state, by casting concrete in between the formwork panels 500 andthe formwork panels 600, the new underground concrete framework 400 isconstructed.

FIG. 5 is a flowchart showing a construction procedure of theunderground structure, and FIGS. 6 to 11 are views showing aconstruction method for the underground structure according to theembodiment performed on the basis of the construction procedure.

Hereinafter, the construction method for the underground structure willbe described, based on the flowchart showing the construction procedurein FIG. 5, with reference to FIGS. 6 to 11.

FIG. 6A is an illustration after the existing underground concreteframework is partially removed, FIG. 6B is an illustration where soil iscarried into the underground pit after the partial removal of theexisting underground concrete framework, FIG. 7A is an illustrationwhere soil is carried into the existing underground concrete framework,FIG. 7B is an illustration where a new pile is set up in part of thefoundation, FIG. 8A is an illustration where the backfill soil isremoved down to a depth to which the existing load-bearing wall and theexisting beam can bear soil pressure, and a strut and a wale for landretaining are set up, FIG. 8B is an illustration where a fluidized soilwall is provided in the underground pit, FIG. 9A is an illustrationwhere a concrete framework of a new pressure plate is provided in theunderground pit, FIG. 9B is an illustration where a new concretefoundation and a slab are provided in the underground pit, FIG. 10A isan illustration where a strut and wale for land retaining is dismantledand removed, FIG. 10B is an illustration where a fluidized soil wall isprovided in the basement, FIG. 11A is an illustration where formworkpanels for a new underground concrete framework are assembled in thebasement, and FIG. 11B is an illustration where the new undergroundconcrete framework is provided in the basement.

<Partial Removal of the Existing Underground Concrete Framework>

First, as shown in FIG. 6A, after an aboveground structure is removed,existing posts 204 constructed in the basement and the underground pitof the existing underground concrete framework 200 are dismantled andremoved, an opening is created by dismantling slabs 205 and 206 in thebasement and the underground pit (the removal may be performed with theexisting beam 201 left so as to receive soil pressure), and an openingis created by dismantling an existing pressure plate 208 partially (stepS100). By dismantling and removing the existing posts 204, spaces forconstructing new underground concrete frameworks in the basement and theunderground pit are secured, and by dismantling the slabs 205 and 206with the existing beam 201 left to create an opening, a work space aresecured.

Moreover, in the embodiment, the existing beam 201, the existingload-bearing wall 202, and the existing foundation 203 of the existingunderground concrete framework 200 are considered as a continuousexisting exterior wall, and utilized as a retaining wall for supportingunderground soil pressure.

<Backfilling Work and Setting Up of a New Pile>

Next, the existing underground concrete framework 200 is backfilled withsoil by carrying soil into the underground pit of the existingunderground concrete framework 200, as shown in FIG. 6B, and carryingsoil into the basement, as shown in FIG. 7A, from the opening created bydismantling the slabs 205 and 206 with the existing beam 201 left (stepS101). This backfilling work can reduce the load of soil pressure on theexisting underground concrete framework 200 utilized as a retainingwall. Further, this backfilling work makes it possible to secure a workspace for heavy equipment (not shown) on the ground and to support theweight of the heavy equipment, and by this heavy equipment, as shown inFIG. 7B, a new pile 405 a can be set up in a hole 405 preliminarilyopened in the existing pressure plate 208 (step S102) . This new pile405 a is for supporting the weight of a new underground concreteframework (mainly a new wall) constructed within the existingunderground concrete framework 200.

In addition, the new pile 405 a is not necessarily set up, depending onload-bearing performances of the existing foundation 203 and theexisting pressure plate 208 of the existing underground concreteframework 200, and a bearing power that is the bearing capacity of theground.

<Removal of Backfill Soil and Setting Up of a Strut and Wale for LandRetaining>

Next, as shown in FIG. 8A, after the new pile 405 a is set up, thebackfill soil is removed from the basement and the underground pit downto a depth to which the existing load-bearing wall 202 and the existingbeam 201 can bear soil pressure (step S103), and the remaining existingbeam 201 is removed. Next, since the soil pressure applied on theexisting underground concrete 200 from the surrounding ground increasesdue to the dismantlement and removal of the existing beam 201 and theremoval of the backfill soil, a strut and wale for land retaining 406 isset up in a part of the existing beam 201 for a temporary aid (stepS104). As the strut and wale for land retaining 406, land retainingH-section steels are used. Therefore, the soil pressure applied on theexisting underground concrete framework 200 can be reduced by the strutand wale for land retaining 406. After the strut and wale for landretaining 406 is set up, the remaining backfill soil is removed (stepS105).

<Construction of a Fluidized Soil Wall in the Underground Pit>

Next, as shown in FIG. 8B, with the existing underground concreteframework 200 and the strut and wale for land retaining 406 supportingthe soil pressure from the ground, the fluidized soil wall 300 isconstructed in the underground pit. In order to construct this fluidizedsoil wall 300, first, a plurality of anchors 307 are driven into theexisting foundation 203 which functions as a wall of the undergroundpit, and separators 501 are coupled with the respective anchors 307(step S106). Next, the above-described formwork panels 500 are assembledso as to fit on the internal shape of the existing underground concreteframework 200, and these formwork panels 500 are kept upright by theseparators 501 (step S107). Further, the formwork panels 500 and theseparators 501, as described above, are fastened to each other withwashers 301 and 302 and nuts 303 to be fixed to each other.

Next, the fluidized soil wall 300 is constructed in the underground pitby filling a space between the existing foundation 203 and the formworkpanels 500 with fluidized soil and solidifying the fluidized soil (stepS108). The fluidized soil used here is slurry backfill soil which ispreliminarily blended with cement in a controlled manner in a plant andwhich can be transported by a fresh concrete mixer vehicle and can becast by a pump. And, by using the formwork panels 500 when constructingthe fluidized soil wall 300, excess water can be discharged through theslits 13 created in these formwork panels 500, and therefore the timerequired to harden the fluidized soil can be shortened.

<Constructing of a New Underground Concrete Framework in the UndergroundPit>

Next, as shown in FIG. 9A, reinforcing bars (not shown) for constructinga new pressure plate 407 are assembled on the existing pressure plate208 in the underground pit (step S109), and concrete for constructingthe new pressure plate 407 is cast (step S110). Next, as shown in FIG.9B, in order to construct a new slab 401 and a new foundation(foundation/underground beam) 404, formwork panels 600 are set up withinthe fluidized soil wall 300 (step S111). First, reinforcing bars areassembled within the fluidized soil wall 300 (step S112), separators 601are coupled with the separators 501 protruding from the formwork panels500, and the assembled formwork panels 601 are kept upright by theseseparators 601. Further, in order to construct the new slab 401 for theunderground pit, formwork panels 600 are provided so as to form a shapeof a slab while being supported by a supporting post. At this time,since the formwork panel 600 can easily be bent along the slits 13created in the formwork panel 600, the formwork panels 600 can beassembled into the shape of a slab. Further, the formwork panels 600kept upright and the formwork panels 600 assembled into the shape of aslab are set up so as to connect to each other.

In the formwork panels 600 thus set up, in order to support lateralpressure applied to the formwork panels 600 when concrete is cast, thepipe 305 extending in the longitudinal direction of the formwork panels600 is fixed on the side of surfaces of the formwork panels 600 by theform ties 306, as described above. Next, the new slab 401 and the newfoundation 404 are constructed by casting concrete (step S113). In thismanner, the new underground concrete framework 400 can be constructed inthe underground pit.

Further, when the new underground concrete framework 400 is constructed,the slits 13 created in the formwork panels 600 can prevent leakage ofconcrete and can discharge excess water in the concrete when theconcrete is cast.

<Building of a Fluidized Soil Wall in the Basement>

Next, as shown in FIG. 10A, the strut and wale for land retaining 406set up to the existing beam 201 is dismantled and removed (step S114),and, as shown in FIG. 10B, a fluidized soil wall 300 is constructed inthe basement.

First, a plurality of anchors 307 are driven into the existing beam 201and the existing load-bearing wall 202 of the existing undergroundconcrete framework 200, and the respective anchors 307 are coupled withseparators 501 (step S115). Next, formwork panels 500 are assembled soas to connect to the formwork panels 500 set up in the underground pit,and kept upright by the separators 501 (step S116). At this time, theformwork panels 500 and the separators 501 are fastened and fixed toeach other by washers 301 and 302 and nuts 303.

Then, a fluidized soil wall 300 is constructed by filling a spacebetween the existing underground concrete framework 200 and the formworkpanels 500 with fluidized soil (step S117). Thus, the fluidized soilwall 300 constructed in the underground pit and the fluidized soil wall300 constructed in the basement are constructed as a continuous singlewall. And, the load of this fluidized soil wall 300 is supported by theexisting beam 201, the existing load-bearing wall 202, and a part of theexisting foundation 203 that constitute the existing undergroundconcrete framework 200.

<Constructing of a New Underground Concrete Framework in the Basement>

Next, as shown in FIG. 11A, on the new underground concrete framework400 constructed in the underground pit, reinforcing bars are assembledto construct a post, a beam, a wall, and a floor that constitute the newunderground concrete framework 400 (step S118). Next, separators 601 arecoupled with the separators 501 protruding from the formwork panels 500of the fluidized soil wall 300 constructed for the basement (stepsS119), and formwork panels 600 are kept upright by these separators 601.Then, formwork panels 600 for constructing the new slab 401 and the newbeam 402 for the basement are assembled (step S120). These formworkpanels 600 are supported by supporting posts.

It should be noted that the formwork panels 600 kept upright and theformwork panels 600 assembled into shapes of a slab and a beam arejoined and assembled so as to obtain a continuous formwork panel 600.

Next, reinforcing bars for the new slab 401 are assembled (step S121),and concrete is cast into a space between the fluidized soil wall 300and the formwork panels 600 (step S122). In this manner, the newunderground concrete framework 400 for the basement can be constructed.Further, the new underground concrete framework 400 constructed in theunderground pit and the new underground concrete framework 400constructed in the basement form a continuous new concrete framework,the weight of which is supported by the new pile 405 a.

As described above, in the construction method for an undergroundstructure according to the embodiment, a new underground structure canbe constructed, without dismantling the existing underground concreteframework, by utilizing this existing underground concrete framework asa retaining wall, and constructing the fluidized soil wall and the newunderground concrete framework within the existing underground concreteframework.

And, since the fluidized soil wall and the new underground concreteframework which are constructed within the existing underground concreteframework are independent of each other via the formwork panel, the loadof the fluidized soil wall can be supported by a portion contacting withthe existing underground concrete framework, and the load of the newunderground concrete framework can be supported by the new pile providedpreliminarily and the foundation of the existing underground concreteframework.

Thus, since the loads of the fluidized soil wall and the new undergroundconcrete framework can be distributed and supported by the existingunderground concrete framework, the load supported by the existingunderground concrete framework can be reduced.

Further, by providing the fluidized soil wall between the existingunderground concrete framework and the new underground concreteframework, the fluidized soil wall makes it possible to reduce thethickness of the new underground concrete framework, as compared withthe construction method in which the new underground concrete frameworkis directly provided in the existing underground concrete framework, andtherefore the amount of concrete can be reduced.

Further, since the formwork panel according to the embodiment is formedby bending a panel steel plate into a substantially angular-wave-likecross sectional shape so as to have a plurality of ridges arranged inparallel at predetermined distances, the strength of the panel itselfcan be reinforced. This makes it possible for the formwork panel tosufficiently bear lateral pressure applied to the formwork panel evenafter filling with the fluidized soil or casting concrete. And, theslits with a predetermined length provided in this formwork panel makeit easy to bend the formwork panel itself, and can promote discharge ofexcess water while preventing leakage of the fluidized soil or concrete.Thus, it becomes easy to bend the formwork panel at a corner, whileconstructing of the fluidized soil wall and the new underground concreteframework can be expedited.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the configuration of a new undergroundstructure according to an embodiment of the present invention;

FIG. 2 is a schematic configuration view of a formwork panel used in theembodiment;

FIG. 3 is a view showing an A-A cross section of the formwork panelshown in FIG. 2;

FIG. 4 is a cross-sectional view showing an X-X cross section of theunderground structure shown in FIG. 1;

FIG. 5 is a flowchart showing the procedure of a construction method ofthe new underground structure according to the embodiment;

FIG. 6 is a schematic illustration of the construction method of the newunderground structure according to the embodiment;

FIG. 7 is a schematic illustration of the construction method of the newunderground structure according to the embodiment;

FIG. 8 is a schematic illustration of the construction method of the newunderground structure according to the embodiment;

FIG. 9 is a schematic illustration of the construction method of the newunderground structure according to the embodiment;

FIG. 10 is a schematic illustration of the construction method of thenew underground structure according to the embodiment; and

FIG. 11 is a schematic illustration of the construction method of thenew underground structure according to the embodiment.

EXPLANATION OF REFERENCE NUMERALS

11: Ridge

12: Rib

13: Slit

14: Lid

16: Groove

31: Top face

32: Side face

200: Existing underground concrete framework

201: Existing beam

202: Existing load-bearing wall

203: Existing foundation (foundation or underground beam)

204: Existing post

205, 206: Slab

208: Existing pressure plate

300: Fluidized soil wall

301, 302: Washer

303: Nut

304: Long nut

305: Pipe

306: Form tie

307: Anchor

400: New underground concrete framework

401: New slab

402: New beam

403: New wall

404: New foundation (foundation or underground beam)

405: New hole

405 a: New pile

406: Strut and wale for land retaining

407: New pressure plate

500, 600: Formwork panel

501, 601: Separator

1. A construction method for a new underground structure by which a newunderground concrete framework is constructed without entirelydismantling and removing an existing underground concrete framework,wherein: a fluidized soil wall is constructed by filling an innercircumferential face of the existing underground concrete framework withfluidized soil, and the new underground concrete framework isconstructed on an inner circumferential face of the fluidized soil wall.2. A construction method for a new underground structure by which anexisting underground concrete framework is partially utilized toconstruct a new underground concrete framework without entirelydismantling and removing the existing underground concrete framework,the method comprising: vertically providing a first formwork body on theside of an inner circumferential face of the existing undergroundconcrete framework at a predetermined distance from the existingunderground concrete framework; filling a space between the existingunderground concrete framework and the first formwork body withfluidized soil to construct a fluidized soil wall; vertically providinga second formwork body on the side of an inner circumferential face ofthe fluidized soil wall at a predetermined distance from the fluidizedsoil wall; and casting concrete in between the fluidized soil wall andthe second formwork body to construct the new underground concreteframework.
 3. The construction method for a new underground structureaccording to claim 2, wherein the first formwork body and the secondformwork body are kept upright by separators.
 4. The construction methodfor a new underground structure according to claim 2, wherein the firstformwork body and the second formwork body are formwork panels formed bybending and cutting a plate-like steel material into a substantiallyrectangular front shape and a substantially angular-wave-likecross-sectional shape.
 5. The construction method for a new undergroundstructure according to claim 3, wherein the first formwork body and thesecond formwork body are formwork panels formed by bending and cutting aplate-like steel material into a substantially rectangular front shapeand a substantially angular-wave-like cross-sectional shape.